This invention relates in general to vehicle steering and suspension systems and, in particular, to a hitch steering suspension system and control circuit especially useful for a four-wheel, two-axle articulately connected tractor-scraper combination.
More specifically, but without restriction to the particular use which is shown and described, this invention relates to a hitch steering, vehicle suspension system for use with a four-wheel, two-axle earthmoving tractor-scraper for steering and controlling bouncing, pitching and rolling motions encountered during operation. In addition, this invention relates to a control system for the vehicle suspension system used on an articulated earthmoving scraper to minimize the bouncing, pitching and rolling motions that occur during operation of a vehicle.
Articulated wheel or tractor scrapers are used for many applications in the construction industry wherein it is necessary to transport heavy loads of material such as dirt and rock over terrain from one location to another, such as in levelling or filling construction or highway sites. Such wheel or tractor scrapers comprise two or four-wheel tractor portions and a two-wheel trailer portion which are articulated about a combined draft and steering coupling, or hitch, formed between the tractor and trailer. The two units are interconnected by a draft frame attached to the trailer which is pivotally mounted on an A-frame, gooseneck coupling of the tractor. The tractor scraper is steered through the manipulation of hydraulic jacks connected between the two portions of the vehicle by turning the tractor portion with respect to the trailer portion about a vertically disposed articulation pivot axis formed by the interconnection between the front and rear portions of the vehicle.
In operating articulated vehicles such as tractor scrapers, it is frequently necessary to allow the tractor and trailer portions of the vehicle to tilt relative to each other about a longitudinal axis extending through the vehicle. Such tilting or rolling is necessary to keep all of the vehicle wheels in contact with the operational surface when travelling over uneven terrain to prevent the loss of tractive power. However, the amount of tilting or rolling movement between the tractor and trailer portions of the vehicle must be controlled in order to maintain vehicle stability. While a limited amount of rolling or tilting of the two portions of the vehicle relative to each other is desirable within predetermined limits, such roll or tilt must be controlled.
In addition to roll or tilt between the tractor portion and the trailer portion of the tractor scraper, bouncing or pitching movement is frequently encountered. Such movement is believed to result from the resiliency of the tires and the weight of the scraper trailer which is suspended between the front and rear wheels of the combination and frequently occurs during hauls at relatively high vehicle speeds. Due to the large size and weight of the tractor scraper, and of the loads transported by it, ordinary shock absorbers or vibration isolators are impractical to resolve the problems created by such bouncing or pitching movement. Such bouncing or pitching movement is uncomfortable and potentially dangerous to the machine operator and, due to the large shock loads imparted by the bouncing trailer portion, can result in damage or failure of structural parts of the vehicle, particularly those closely associated with the load carrying body.
A number of attempts have been made to resolve or control the rolling, bouncing and pitching conditions encountered in tractor-trailer combinations. One such control system has been illustrated in the inventor's U.S. Pat. No. 4,279,319, the disclosure of which is incorporated herein by reference. For example, in U.S. Pat. No. 4,279,319 there is utilized an arrangement for controlling a vehicle axle suspension system wherein a plurality of pitch damping and roll or tilt damping hydraulic cylinders are operatively connected to portions of the vehicle for dampening undesirable movement.
Another control system is illustrated in the inventor's U.S. Pat. No. 4,201,273, the disclosure of which is also incorporated herein by reference. In U.S. Pat. No. 4,201,273, there is utilized a first pair of hydraulic cylinders to control and dampen vertical bounce movement and a second pair of hydraulic cylinders for supplementing the first pair of cylinders to control vertical movement between the tractor drive wheels and to dampen tilting and rolling motion between tractor and trailer about their common longitudinally extending axis.
Other attempts have been made to resolve the bouncing and pitching problems associated with tractor-trailer units. For example, attempts have been made to utilize a separate tractor drive wheel axle A-frame pivotally connected to the tractor main frame to allow for vertical movement of the tractor drive wheels relative to the frame. In U.S. Pat. No. 3,865,205, there is disclosed such a separate drive wheel axle frame which is pivotally connected to the front portion of the tractor main frame to extend rearwardly to a position beneath the hitch assembly. It is the object of such a coupling arrangement to obtain better weight distribution by permitting the vehicle engine to be mounted on the rear portion of the tractor unit and to allow the vehicle operator to be positioned forwardly of the engine for increased visibility.
Other examples of steering and suspension systems are described in U.S. Pat. Nos. 2,638,998, 3,032,135 and 3,828,882. These references show various arrangements of swing arms pivotally connected to intermediate members for movement about a vertical articulation pivot point and including steering cylinders to move the swing arms and intermediate members for steering the vehicle.
While each of these patents discloses apparatus that attempt to resolve the problems associated with steering tractor trailer units and the controlling bouncing and pitching movement thereof have been somewhat successful, such disclosures do not provide for completely controlling the rolling or tilting conditions between the tractor and trailer portions of the articulated vehicle.